Many phosphate and phosphorothioate esters are known to have pesticidal activity of one kind or another. Various related sulfur-substituted phosphorothioate esters are also known to be active insecticides and miticides. A number of such esters are described in U.S. Pat. No. 3,042,703, West German Pat. No. 1,183,494 and Japanese Pat. No. 11880/66. These patents all disclose esters having the general structural formula ##STR1## where the phenyl group may have one or more inert substituents, R is a lower alkyl group, usually methyl or ethyl, R' is also a lower alkyl group, and n is zero, one or two. No compounds are shown where R' is a tertiary alkyl group.